Comment Linking And Trackbacks With False Urls

Since I started blogging regularly, I've noticed an increase in the number of people trying to comment or trackback to my posts using anchor text links and urls that don't actually go anywhere.

I've also had my contact form completed with letter jumbles that make no sense and urls which are gobbledegook and obviously go nowhere. At first, I thought the latter were just people messing around but it's quite clear from the number and the uniformity of the entries that there's more to it than that.

Can anyone tell me what either of these two strategies is hoping to achieve, bearing in mind that I have captcha and moderation on? Is it just people taking an optimistic punt or an automated system gone wrong or something else entirely?

In my attempts to understand what works, I thought it might be an idea to try to grasp what doesn't...